1. Field of the Invention
The present invention relates to a liquid crystal apparatus using a liquid crystal material and a polymer material. More specifically, the present invention relates to a photopolymerizable resin material composition for forming a liquid crystal display apparatus having liquid crystal regions surrounded by polymer walls and to a matrix-type liquid crystal display apparatus.
2. Description of the Related Art
As for methods for producing a liquid crystal display apparatus, one for producing a polymer-dispersed liquid crystal display apparatus has been known. According to this method, a mixture of a photocurable or thermosetting resin material is used. Among the mixture, only the resin material is cured so as to be phase-separated from the liquid crystal material, whereby liquid crystal droplets are formed between cured and deposited polymers.
In a conventional liquid crystal display apparatus, orientation of liquid crystal molecules and display color are likely to change during a pen input and cell thickness is likely to change in upper and/or lower portions of a display apparatus due to weight, causing unevenness in the display. However, in the polymer-dispersed liquid crystal display apparatus produced by the phase-separation method, liquid crystal molecules are held in polymers, so that cell thickness is not likely to change, resulting in enhanced display stability of the liquid crystal apparatus with respect to an external force.
As a polymer-dispersed liquid crystal display apparatus; Japanese National Publication No. 58-501631 discloses one displaying a scattered state under the application of no voltage, in which a refractive index of liquid crystal is not matched with that of a polymer and displaying a transparent state under the application of a voltage, in which the refractive index of the liquid crystal changes so as to be matched with that of the polymer.
As methods for forming the polymer-dispersed liquid crystal display apparatus, two methods have been disclosed: Japanese National Publication No. 61-502128 discloses that UV-rays are radiated upon a mixture of liquid crystal and a photocurable resin so that the liquid crystal is phase-separated from the photocurable resin three-dimensionally; and Japanese Laid-Open Patent Publication No. 2-310520 discloses that UV-rays are radiated upon a mixture of a photocurable resin containing liquid crystal and a (meth)acrylate compound so that the liquid crystal is phase-separated from the polymer three-dimensionally. These apparatuses electrically control a scattered state and a transparent state, and therefore, they use materials capable of forming smaller liquid crystal droplets so as to enhance scattering characteristics under the application of no voltage.
In the case where a conventional polymer-dispersed liquid crystal display apparatus is to be utlized a mode in which liquid crystal molecules are required to be aligned in different directions relative to the substrates sandwiching the liquid crystal, such as a TN mode and an STN mode, it is difficult to form liquid crystal droplets in a uniform manner, to exactly control the positions of the liquid crystal droplets, and to perform alignment treatment of the liquid crystal molecules due to the limitations of the production method. This causes various problems. For example, in the conventional polymer-dispersed liquid crystal display apparatus, it is difficult to form liquid crystal droplets in a uniform manner and to exactly control the positions of the liquid crystal droplets. Therefore, a drive voltage varies depending upon the liquid crystal droplet. This causes a lack of abruptness in the threshold response for various electrooptical characteristics, relatively increased drive voltage, and difficulty in enlarging a screen in a high definition state.
Furthermore, since a number of liquid crystal droplets having a low light-scattering ability are present, contrast of the display relatively decreases.
Furthermore, since it is difficult to control the orientation of liquid crystal molecules, viewing angle characteristics are poor and contrast decreases due to depolarization caused by scattering at interfaces between the liquid crystal molecules and the polymer. Specifically, when the polymer is present between the substrates and the liquid crystal in the polymer dispersed liquid crystal apparatus, alignment treatment cannot be performed with respect to the substrates. In order to solve the problem of scattering at interfaces between the liquid crystal molecules and the polymer, the interfaces therebetween in pixels may be reduced. However, according to a conventional method, since liquid crystal droplets are naturally formed, it is difficult to reduce the interfaces.
Furthermore, in a liquid crystal apparatus using ferroelectric liquid crystal, shock resistance is weakened because of the high regulating ability of a liquid crystal phase (smectic phase) to be used.
In order for the above-mentioned polymer dispersed liquid crystal display apparatus to have regulating ability, it has been disclosed to use a photomask through which UV-rays are radiated to a mixture of liquid crystal and a photocurable resin material so as to deposit a polymer.
Japanese Laid-Open Patent Publication No. 1-269922 discloses a method including the steps of radiating UV-rays upon the mixture through a photomask, removing the photomask, and then radiating UV-rays onto portions which have been covered with the photomask, thereby forming regions having different characteristics. Also disclosed is a liquid crystal display apparatus produced by the method. This apparatus is the type driven in a scattering-transmission mode.
Japanese Laid-Open Patent Publication No. 5-257135 discloses a liquid crystal device produced by injecting a mixture of a liquid crystal material and a photocurable resin between substrates on which an alignment film having an alignment regulating force is respectively formed and using UV-rays to radiate the mixture through a photomask. This device is the type for static drive in which patterning is performed from outside a cell because threshold characteristics inside the photomask are different from those outside the photomask.
In general, in order to improve viewing angle characteristics in a liquid crystal apparatus of a non-scattering mode by enhancing an orientation state of liquid crystal molecules, the liquid crystal molecules are required to be aligned in at least three directions in the pixels. For example, referring to FIG. 1A-1C, liquid crystal molecules 13 are aligned differently depending upon the liquid crystal region surrounded by a polymer 12 between two substrates 11. In such an orientation state, an apparent refractive index of the liquid crystal molecules is averaged when they are seen in directions A and B in an intermediate gray scale. As a result, the contrasts seen from both directions A and B become identical, and viewing angle characteristics are enhanced, compared with a liquid crystal display apparatus in a TN mode shown in FIG. 2A-2C.
Japanese Laid-Open Patent Publication Nos. 4-338923 and 4-212928 disclose wide viewing angle liquid crystal display apparatuses in which viewing angle characteristics are improved by attaching two polarizing plates to the polymer dispersed liquid crystal display apparatus so that the plates are orthogonal to each other.
Furthermore, Japanese Laid-Open Patent Publication No. 5-27242 discloses a method for producing a non-scattering liquid crystal apparatus made of a composite material of liquid crystal and a polymer material, utilizing phase separation of a mixture containing liquid crystal and a photocurable resin. According to this method, the generated polymer randomly align liquid crystal domains and liquid crystal molecules rise in different directions depending upon each domain under the application of a voltage. Therefore, an apparent refractive index from each direction becomes equal, and viewing angle characteristics are improved in an intermediate gray scale.
In recent years, the present inventors found the following: By using a photomask during photopolymerization of a mixture of liquid crystal and a photocurable resin material, liquid crystal molecules in a liquid crystal device to be obtained are omnidirectionally aligned (in a spiral shape) in pixel regions. This spiral orientation of the liquid crystal molecules is controlled with a voltage, whereby the liquid crystal molecules move as if part of umbrellas which are opened or closed. Thus, a matrix-type liquid crystal display apparatus with improved viewing angle characteristics is obtained (Japanese Laid-Open Patent Publication No. 6-301015). However, this apparatus has problems with respect to contrast, response time, roughness, and the like because of a resin material mixed into a liquid crystal material.
Thus, as described above, in a polymer dispersed liquid crystal display apparatus in a non-scattering mode, the following methods have been demanded: a method for forming liquid crystal droplets in a uniform shape and exactly regulating the positions of liquid crystal droplets, a method for aligning liquid crystal molecules omnidirectionally in pixels which is required for improving viewing angle characteristics, and a method for preventing contrast from decreasing due to depolarization caused by scattering at interfaces between liquid crystal molecules and a polymer.